Still unplaced

Your report on communications satellites states: "Iridium's constellation of 66 working satellites and six orbiting spares was completed last week with the launch of five satellites" (This Week, 19 September, p 16).

Unfortunately, this is not quite correct, since launching five satellites does necessarily place them in their correct positions. The gaps that have appeared in the working network are distributed among several of the six orbital planes occupied by the Iridium satellites.

Getting the replacements to the right positions within those planes is likely to take considerable time and effort.

I expect the 1 November deadline to pass with some locations unfilled and the system only 90 to 95 per cent operational. This is still an achievement, considering it is only 18 months since the first Iridium was launched.

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